The present invention is directed to an improved torque transmission driver used to transmit torque from a torque generating source, such as a power drill, to a fastener for assembly of a structure or device, most notably where the fasteners are small less than size 10.
Torque transmission drivers have been commonly used in assembling structures and devices with threaded fasteners such as screws and bolts. Such torque transmission drivers transmit the torque created by a torque generator to the fastener to thread a fastener into an assembly. Various such torque transmission drivers have been provided in the past, usually having the shape of a drive end complementary to a recess in or projections from the heads of fasteners, with which they are used. Examples are drill chucks and screw drivers.
To illustrate, U.S. Pat. No. 2,397,216 issued in 1946 discloses a number of forms or shapes of torque transmission drive systems. Known are the hex-type and cruciform-type torque transmission driver such as the PHILLIPS® torque drive system. Also, U.S. Pat. No. 3,584,667 shows a torque transmission driver which has been widely used in automotive, aerospace and appliance manufacture and marketed under the brand name TORX®. Various lobe-type torque drive systems similar to the TORX® drive system are also shown in U.S. Pat. Nos. 5,025,688, 4,269,246, 4,006,660, 3,885,480, 2,969,250 and 2,083,092 issued between 1991 and 1938. See also U.S. Patent Application Pub. No. US 2010/0129176 published May 27, 2010.
Prior art torque transmission drivers were made with the key shape of the driver well defined to engage a fastener recess at and near the terminal end of the nib, away from the first end portion of the driver for engaging the torque transmission source. The bit of the driver would transition from the key shape to engage the recess of the fastener to a shape to conform generally to the shape of the first end portion. This way of making such past drivers provided a bit on the driver to engage a fastener along a limited proportion of the nib, and requiring the torque transmission driver to have a longer nib in order to fully engage the drive recess of a fastener. This required a relatively long bit generally 0.60 inch or greater and resulted inefficient driver and method of making the driver.
Also traditional forging methods is often insufficient for precision drives having a small size, such as size 10 and smaller. Forging such drivers is not sufficiently precise so a forged nib may not properly engage the drive recess of a fastener. This may be because the lobes of the key drive or valleys there between are missized or misaligned. Further, even if the key drive is manufactured to the precise tolerances, the tapered aspect of the forged nib may result in the driver not seating properly in the drive recess of fasteners. This misalignment may not be immediately noticeable because the driver may still function to drive fasteners due to the tapered key drive or the nib. However, because of the imprecision in the key shape, the driver may wear earlier and more than expected, fasteners fastened with the driver may strip out more often, and/or the driver may not be able to tightened fasteners to a uniform or accurate torque. Moreover, particulate matter is generated during strip out and wear which is particularly harmful in electronic devices. This creates the potential for inefficiencies and losses in the use of torque transmission drivers.
Despite the previous developments in torque transmission drivers, there remains a need for a torque transmission driver with the capability to provide better torque transmission capability, and to reduce strip out of the recess of the fastener and reduce variation in driver torque failures. This need has been particularly acute and long recognized in torque transmission drivers for small fasteners less than size 10, where the recess in the head of the fastener is less than 0.100 inch, or less than 0.060 inch, in the major dimension. These torque transmission driver have been generally difficult to engage and maintain stabilized with the small fasteners during installation, have had reduced engagement with the fasteners limiting the amount of torque that could be transmitted from the driver to the fastener, and involved fine threads on the fasteners that could more readily be cross threaded and/or stripped out during installation. As a result, in the past special installation tools have had to be used for these fasteners, which in turn limited the serviceability and repair ability of the structure or device assembled using the drivers and fasteners. Moreover, because of variability in installation torque, the quality control of the assembly was difficult if not impossible to maintain with such previous transmission torque drivers. Finally, the improved driver increases the tolerances that can be maintained within the drive, and reduces particulate generation due to strip out and wear, which is particularly problematic in electronic devices.
A torque transmission driver is presently disclosed that comprises a shaft having a first end portion adapted to receive and transmit torque from a torque generating source to the driver, and a second end portion forming a nib having a five or six-lobe key-shape adapted to fit a recess in the fastener, wherein the second end portion is equal to or less than 0.050″ in length and having lobes of substantially the same form along the entire second end portion.
Additionally, the key-shape with a major diameter and a minor diameter may include a taper of no greater than 55° at the base of each lobe where the second end portion of driver reaches the first portion of the driver. Further the shape of that taper may be convex.
Also disclosed is a torque transmission driver comprising in addition a protruding lead end on the second portion initiating from the key shape of the second portion and transitioning to a cross-sectional shape different from the key shape with a taper at an angle between 10° and 30° from a plane perpendicular to the drive axis of the driver and with a substantial portion thereof adapted to complement and frictionally engage at least a portion of a recess in a fastener.
In further aspects, the key-shape is sized to a size 10 or smaller driver; a size 6 or smaller driver; a M6 or smaller driver; or a M3.5 or smaller driver. Additionally, the nib may have a length equal to or less than 0.033″.
Also disclosed is a method of making a torque transmission driver. The method includes the steps of providing a torque transmission driver blank including a first end portion for receiving and transmitting torque from a torque generating source, providing a second end portion forming a nib having a five or six-lobe key-shape adapted to fit a recess in the fastener where the second end portion is equal to or less than 0.050″ in length and has lobes of substantially the same form along the entire second end portion the first end, forming a taper in the first end portion adjacent the second end portion extending from the key shape of the second end portion. The taper is no greater than 55° at the base of each lobe extending from the major diameter to the minor diameter. The length of the nib of the second end portion is equal to or less than 0.050″ exclusive of the taper; or equal to or less than 0.030″ not including the taper. The taper also may be convex.
Further, this method may include the additional step of forming a protruding lead end in the second end portion, the protruding lead end initiating from the key shape of the second end portion and transitioning to a cross-sectional shape different from the key shape with a taper at an angle between 10° and 30° from a plane perpendicular to the drive axis of the driver and with a substantial portion thereof adapted to complement and frictionally engage at least a portion of a recess in a fastener.